1. Field of the Invention
The present invention is broadly concerned with an improved fluid pumping system having a fluid seal assembly that can be used to seal an opening along a rotatable shaft in fuel pumps and the like. More particularly, the invention is concerned with a fuel pump seal assembly having multiple sealing elements including a fluid chamber that acts as a fluid seal to result in improved fuel economy and horsepower performance by isolating the fuel chamber from outside sources of air.
2. Description of the Prior Art
Internal combustion engines are typically supplied by a fuel pumping system that may include a number of sequentially interconnected pumps each having rotatable shafts which require seal assemblies to prevent leakage. For example, a pump may move fuel from a fuel tank through a filter assembly to the intake of a transfer pump. The transfer pump may supply a pressure regulated stream of fuel to a distribution pump or in-line multicylinder pump which feeds a high pressure diesel injector rail system. In the event that air enters the sealed fuel supply system, severe engine problems can develop, such as a corresponding drop in fuel economy and horsepower, difficult starting, smoking exhaust, a spongy throttle, diesel knock or engine misfire, stalling, and low idle RPM surges. Therefore, fuel pumps typically have a seal assembly that is intended to isolate separate bodies of fluid, such as a liquid fuel and atmospheric gases, which would otherwise bleed together across various openings that accommodate a rotatable shaft.
Previous pump seal assemblies have typically used one or two neoprene seals that are press-fit into an aperture in a housing wall. Different types of fluid are thereby isolated across opposed faces of the wall. In the case where two neoprene seals are utilized, these may be spaced apart along the length of the shaft to define a cavity therebetween, and the housing wall may have a vent opening that communicates between the outside atmosphere and the cavity. This vent opening is also known as a weep hole, because it is possible to see liquid pouring out of the hole after one of the seals has failed. In the dual-deal system, one of the seals may prevent fuel from communicating with the vent hole, and the other seal may prevent lubricating oil from and accessory drive mechanism from communicating with the vent hole. It is typically assumed that the seal assembly is completely intact unless liquid is visibly present at the exterior weep hole, since the pumps typically operate with fuel circulated in contact with the seal for cooling purposes at positive internal pressures ranging between about 3 to 5 psig.
In tractor-trailer diesel engine applications, these dual seals are not normally expected to fail prior to having travelled between about 40,000 to 100,000 or more miles. A failure of the seal assembly in a diesel fuel pump is normally assumed to be noticeable as a leak from the weep hole requiring replacement of the seal or the entire pump.